Thanks Ron, your monitoring of this forum is real bonus as it gives hope !
I tried out a few other things, I changed the IP address of my MSS+ and Mac from its static 10.x.x.x address to a new static 192.168.1.x. The mac could see the MSS+ share for a few moments and then it disappeared (?). That trick never worked a second time.
I still think there is something wrong with my Mac. The command: mDNS -B _daap._tcp. local finds nothing on the LAN. I tried disabling all the LAN interfaces and removing the preferences.plist to work from a new “blank sheet”.
I read Apple is due to release 10.4.10, so may be that update will slip something in.
I’ll keep hunting, but if you could cross check with yours it would be great.